Wedden S E
Department of Anatomy and Biology, Middlesex Hospital Medical School, Cleveland St, London, UK.
Development. 1987 Mar;99(3):341-51. doi: 10.1242/dev.99.3.341.
The development of the chick face involves outgrowth of buds of tissue, accompanied by the differentiation of cartilage and bone in spatially defined patterns. To investigate the role of epithelial-mesenchymal interactions in facial morphogenesis, small fragments of facial tissue have been grafted to host chick wing buds to continue their development in isolation. Fragments of the frontonasal mass give rise to typical upper-beak-like structures: a long central rod of cartilage, the prenasal cartilage and an egg tooth. Meckel's cartilage, characteristic of the lower beak, develops from fragments of the mandible. Removal of the ectoderm prior to grafting leads to truncated development. In fragments of frontonasal mass mesenchyme only a small spur of cartilage differentiates and there is no outgrowth. The mandible is less affected; a rod of cartilage still forms but the amount of outgrowth is reduced. Retinoid treatment of chick embryos specifically affects the development of the upper beak and outgrowth and cartilage differentiation in the frontonasal mass are inhibited. The mandibles, however, are unaffected and develop normally. In order to investigate whether the epithelium or the mesenchyme of the frontonasal mass is the target of retinoid action, recombinations of retinoid-treated and untreated facial tissue have been grafted to host wing buds. Recombinations of retinoid-treated frontonasal mass ectoderm with untreated mesenchyme develop normally whereas recombinations of untreated ectoderm with retinoid-treated mesenchyme lead to truncations. The amount of outgrowth in fragments of mandibular tissue is slightly reduced when either the ectoderm or the mesenchyme has been treated with retinoids. These recombination experiments demonstrate that the mesenchyme of the frontonasal mass is the target of retinoid action. This suggests that retinoids interfere with the reciprocal epithelial-mesenchymal interactions necessary for outgrowth and normal upper beak development.
鸡面部的发育涉及组织芽的生长，并伴随着软骨和骨在空间上按特定模式分化。为了研究上皮-间充质相互作用在面部形态发生中的作用，已将面部组织的小片段移植到宿主鸡翼芽上，使其在隔离状态下继续发育。额鼻突的片段产生典型的上喙样结构：一根长的中央软骨棒，即鼻前软骨和一个卵齿。下颌骨特有的梅克尔软骨由下颌骨片段发育而来。移植前去除外胚层会导致发育不全。在额鼻突间充质的片段中，只有一小段软骨分化，且没有生长。下颌骨受影响较小；仍会形成一根软骨棒，但生长量减少。用类视黄醇处理鸡胚会特异性地影响上喙的发育，额鼻突中的生长及软骨分化受到抑制。然而，下颌骨未受影响且发育正常。为了研究额鼻突的上皮还是间充质是类视黄醇作用的靶点，已将经类视黄醇处理和未处理的面部组织重组体移植到宿主翼芽上。经类视黄醇处理的额鼻突外胚层与未处理的间充质的重组体正常发育，而未处理的外胚层与经类视黄醇处理的间充质的重组体则导致发育不全。当外胚层或间充质用类视黄醇处理时，下颌组织片段中的生长量会略有减少。这些重组实验表明，额鼻突的间充质是类视黄醇作用的靶点。这表明类视黄醇干扰了生长和正常上喙发育所需的上皮-间充质相互作用。
